On-Instrument WFS

Some of the Gemini facility instruments have on-instrument wavefront sensors. For the optical instruments (e.g. GMOS) the OIWFS is a CCD. For the near-IR instrument NIFS the OIWFS is itself a near-IR detector. NIRI, Phoenix, and the mid-IR instruments and visiting instruments have no OIWFSs and use the PWFSs.

As they are located very much closer to the instrument focal plane than the PWFS, the OIWFS have a much smaller vignetting footprint, albeit with a more limited patrol field. The optical OIWFSs have higher sensitivity than the PWFSs, which compensates for their smaller patrol fields. See the specific instrument pages for availability of each OIWFS and details of patrol field restrictions and sensitivity.